Introduction to GPRS DTU and its working principle This article originates from Xiamen Cai Mao Communication Technology Co., Ltd.

GPRS DTU full name GPRS data transmission unit, in the country currently has a more explicit agreement for GPRS DTU: GPRS DTU is a GPRS wireless device that is specifically used to transmit serial data through the GPRS network.

The four core functions of GPRS DTU:

1) Internal Integrated TCP/IP Stack
GPRS DTU encapsulates PPP dial-up protocol and TCP/IP protocol stack and has embedded operating system. From hardware, it can be regarded as a combination of embedded PC and wireless GPRS MODEM; it has GPRS dial-up Internet access and TCP/IP data. The function of communication.

2) Provide bidirectional conversion function of serial data
GPRS DTU provides a serial communication interface, including RS232, RS485, RS422, etc. are all commonly used serial communication methods, and GPRS DTU design in most of the serial data is designed as a "transparent conversion" mode, which means that GPRS DTU can The raw data on the serial port is converted into TCP/IP data packets for transmission without changing the original data communication content. Therefore, the GPRS DTU can be connected to various user equipments that use the serial communication without changing the user equipment.

3) Support automatic heartbeat and stay permanently online
One of the advantages of the GPRS communication network is that the GPRS terminal equipment is permanently online, so typical GPRS DTUs are designed to support the permanent online function, which requires the DTU to include automatic dialing on power and use of heartbeat packets to maintain permanent online (when long When there is no data communication, the mobile gateway will disconnect the DTU from the center. The heartbeat packet is a small data packet sent between the DTU and the data center before the connection is disconnected to keep the connection from being disconnected. It supports automatic disconnection of the disconnected line. , automatic redial and other features.

4) support parameter configuration, permanent preservation
As a communication device, GPRS DTU has a wide range of applications. In different applications, the IP address and port number of the data center and the baud rate of the serial port are different. Therefore, the GPRS DTU should support parameter configuration and store the configured parameters in internal permanent storage devices (generally FLASH or EEPROM, etc.). Once powered on, it will automatically work according to the set parameters.

GPRS DTU extensions:

The more professional GPRS DTU also provides some extended functions, including: support for data center domain name resolution, support for remote parameter configuration / remote firmware upgrade, support for remote SMS / phone wake, support for local serial firmware upgrade, provide SMS channels, provide DTU online / Offline level indication, etc.

These extended functions can enhance the reliability of the system, as well as user-friendly use and maintenance.

GPRS DTU work process description:

After the GPRS DTU is powered on, it first reads out the working parameters saved in the internal FLASH (including GPRS dialing parameters, serial port baud rate, data center IP address, etc., which have been configured in advance).

The GPRS DTU lands on the GSM network and performs GPRS PPP dialing. After successful dialing, the GPRS DTU will get an internal IP address (typically 10.XXX) randomly assigned by the mobile. In other words, the GPRS DTU is in the mobile intranet, and its intranet IP address is usually not fixed and changes with each dialing. We can understand that GPRS DTU is now a device within a mobile internal LAN, through the mobile gateway to achieve communication with the external Internet public network. This is similar to the way a computer in a LAN accesses an external network through a gateway.

The GPRS DTU initiatively initiates a communication connection with the data center and maintains the communication connection. Because GPRS DTU is in mobile intranet, and IP address is not fixed. Therefore, the data center can only be actively connected by the GPRS DTU, and cannot be actively connected to the GPRS DTU by the data center. This requires the data center to have a fixed public IP address or a fixed domain name. The public network IP address or fixed domain name of the data center is stored as a parameter in the GPRS DTU, so that once the GPRS DTU is successfully dialed up, it can actively connect to the data center.

Specifically, the GPRS DTU initiates a TCP or UDP communication request to the data center through the IP address of the data center (if the center domain name is used, first the center IP address is resolved through the center domain name) and the port number and other parameters. After receiving the response from the center, the GPRS DTU thinks that the handshake with the center is successful, and then keeps this communication connection in existence. If the communication connection is interrupted, the GPRS DTU will immediately shake hands with the center again.

Since the TCP/UDP communication connection has been established, data can be bidirectionally communicated.

For the DTU, as long as the establishment of a two-way communication with the data center, the conversion of the user's serial data and GPRS network data packets is relatively simple. Once the user's serial data is received, the DTU immediately encapsulates the serial data in a TCP/UDP packet and sends it to the data center. On the contrary, when the DTU receives the TCP/UDP packet sent from the data center, the data content is taken out from the DTU and immediately sent to the user equipment through the serial port.

Through the wired data acquisition center, two-way communication with many GPRS DTUs simultaneously. This is the most commonly used method in the current GPRS DTU application system.

Power Cable

AC (Alternating Current) Power cord is to transmit high voltage. It is used to drive machinery or home appliances. Since AC Power Cord is output of high voltage electric power, there is a risk of electric shock injury, therefore, All the AC power cord must comply with safety standard to produce. DC (direct Current) power cord is used to the applicance with lower voltage mostly, so safety requirement is less stringent.

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